is a specific kind of: affair, function, occasion, social function, social occasion.

is a broader term that covers: circumstance | funeral, obsequy | hymeneals, nuptials, wedding, wedding ceremony | pageant, pageantry | dedication | opening | commemoration, memorialisation, memorialization | military ceremony | induction, initiation, installation | exercise | fire walking | formalities, formality | Maundy | potlatch ... show more.

derivation: celebrate, keep, observe | ceremonial.